Press Release
Long-distance test monitors physiological safety: Measurable progress
- Physiological safety, an important development goal at Mercedes-Benz
- Seven-week practical monitoring test with more than 20 drivers
- Important stress indicator ??????????????????????????????????????? heart rate ??????????????????????????????????????? lowest in the new S-Class
Best possible cooperation between driver and vehicle has always been a top priority at Mercedes-Benz. Mercedes-Benz develops vehicles which are less stressful to drive, and is a pacemaker in the development of state-of-the-art driver assistance systems.
For the past 15 years Mercedes-Benz has referred to these activities under the name "physiological safety", also sometimes known as ???????????????????????????????????driver-fitness safety????????????????????????????????.
Physiological safety, an integral part of Mercedes-Benz's broad-based safety philosophy, also plays an important role in preventing accidents. Because drivers who remain mentally and physically fit at the wheel will have sufficient energy in reserve to respond quickly and correctly in critical situations. Mercedes passenger cars are designed to maintain and in some cases even improve their driver's physiological fitness.
Physiological safety ??????????????????????????????????????? along with handling safety, operating safety and perceptual safety ??????????????????????????????????????? is therefore one of the key components of active safety. At Mercedes-Benz, physiological safety is defined as comprising
- systems which keep the driver in good psychophysical condition;
- all activities and systems which serve to reduce driver stress and thus to reduce the probability of driver errors;
- all technical features which promote relaxed, stress-free driving and which help to make the driving task easier.
Thus physiological safety is a broad-based and interdisciplinary development goal. Starting with the interior dimensions it includes all aspects relating to suspension comfort, climate comfort, seat comfort and noise. It also includes the development of intelligent assistance systems which automatically perform certain tasks while the vehicle is en route. Critically, it also involves ensuring perfect interaction between all the various individual systems and features, with the aim of putting less strain on the driver and conserving his energies. This requires extensive experience and competence in overall vehicle design, a field which is given high priority at Mercedes-Benz.
The new S-Class leverages the development engineers' long-standing experience and offers greater physiological safety than ever before. This can be seen in the results of a seven-week driver-monitoring test carried out by DaimlerChrysler Research in Berlin with over 20 drivers. The drivers tested the new S-Class and two competitor models on the route Berlin???????????????????????????????????????Leipzig???????????????????????????????????????Dresden-Berlin. The drive comprised motorways, medium-grade extra-urban roads and urban roads. In total approximately 35,000 kilometres were clocked up in the course of the test.
Physiological monitoring en route
The DaimlerChrysler researchers have developed a variety of methods which allow them to objectively evaluate the physiological safety of a vehicle. In particular these include recording of speed data and braking and steering inputs, and physiological measurement of typical stress indicators, most notably heart rate. Heart rate is a reliable, unconscious indicator of stress which is capable of being continuously monitored. Increases in heart rate can be caused by a variety of factors such as a hectic schedule, high traffic volumes or low emotional well-being. Vehicle-specific factors also play a part ??????????????????????????????????????? for example high interior noise levels, inadequate ventilation, a poor seating position, poor visibility or uncomfortable suspension. These aspects are therefore central to Mercedes-Benz's focus on highest standards of physiological safety.
Data acquisition computers on board the test vehicles linked to physiological monitors hooked to the drivers' belts take approximately 90 readings per second while the drivers are at the wheel. The readings provide extensive information about the physical status of the drivers and allow precise and representative measurement of the influence of vehicle technologies on driver behaviour and driver performance.
A special aerial on the rear windscreen also linked the data acquisition system to the satellites of the Global Positioning System (GPS). The positioning coordinates are collected in parallel with the physiological readings and recording of technical parameters, so that during subsequent evaluation the researchers can establish which sections of the route correlated to the highest stress levels.
Online status checks on driver mood
As understood by the Mercedes researchers, the physiological status of drivers includes more than just physical fitness and performance. It also includes emotional factors like mood, tension or motivation, since these factors too help to determine the subject's responsiveness and fitness. These aspects are measured in psychoanalytic interviews before and after each drive and by online status checks en route. At 30-minute intervals, the subjects were required to respond to eight questions about their current mood, recording their answers by pressing a touchscreen on the dashboard. The questions included "How tired do you feel?" and "how positive is your mood?". Possible answers ranged from "1", indicating "not at all", to "6" or "very".
In this way the physiological safety researchers were able to establish whether drivers responded positively (eustress) or negatively (distress) to stress situations which arose en route. The physiological readings like heart rate are an indicator only of the extent of the driver's reaction or arousal and do not reveal anything about its qualitative nature or its effect on driver responsiveness.
As part of their long-term tests the researchers also use a further method to ascertain fatigue and overload. This involves looking deep into the eyes of the test subjects. In the "pupillographic sleepiness test", pupil diameter and oscillation is recorded by infrared light over an eleven-minute period and the results compared with empirical mean values. When the subject is fatigued, the pupil oscillates more strongly at the edges than when the subject is alert. Fatigue also results in a change in pupil diameter. This test, which is carried out before and after the driver-monitoring test, provides objective information, since pupil reactions are controlled by the autonomic nervous system and therefore cannot be manipulated.
Heart rate up to six per cent lower in the new S-Class
As the results of the driver-monitoring test demonstrate, the intelligent overall design of the new S-Class promotes a high level of physiological safety. The average heart rate of the test subjects was below that recorded in competitor models. In high-speed motorway driving for example, the average heart rate in the new S-Class was 79.6 beats per minute ??????????????????????????????????????? up to six per cent (or five beats per minute) ??????????????????????????????????????? lower than that recorded in other saloons in this class.
The major advances Mercedes-Benz has achieved over the last 15 years in the field of physiological safety are also evident when the readings are compared with those obtained in long-distance monitoring tests with earlier S-Class saloons. For example the average heart rate in the new S-Class was up to eight per cent (or 6.8 beats per minute) down on the readings recorded in past tests with the W 126 series S-Class.
